1. Field of the Invention
This invention relates to electroacoustic transducers, and more particularly, to a dual mode piezoelectric transducer and method for generating an alerting signal in an output mode and providing a switching signal in an input mode.
2. Background Discussion
Piezoelectric transducers have been increasingly used in signalling devices such as communication receivers, watches, and other alerting apparatus which employ a single tone alert signal. These transducers generate an acoustic alert signal when stimulated by an electrical voltage. Examples of such transducers are those described in U.S. Pat. Nos. 4,413,198 and 4,240,002. One problem with such alerting transducers is that they occupy relatively large amounts of space compared to the actual electronic circuitry required to operate these signalling devices. Thus, as modern signalling devices become smaller, the alerting transducer size becomes an increasing problem. Another problem with these alerting transducers is that they provide only an output alert signal.
Additionally, numerous types of switches have also been employed on these signalling devices to provide inputs to the processing circuitry. Examples of such prior art input switches are those disclosed in U.S. Pat. Nos. 3,643,041 and 3,684,842. One problem with using electronic switches is that they must constantly be powered from an extrinsic power supply for detecting a change in their switch status. Even when the switch is used as an on/off switch, power is continuously supplied from the signalling devices power supply such as a battery. Thus, when the user turns off his device and stores it for a long period of time, the battery will eventually become discharged.
In some applications, it is desirable to consense battery energy by having a switching device which provides an electrical signal which operates to turn on the prorcessing circuitry in the absence of any extrinsic power. I would also be highly desirable to conserve space by combining in one transducer the function of a switch and an alert signal generator.